This handsome guy has delt with some rough patches!
As most already know he was apart of a sub group called EXO-M. long story short there was a lot of controversy about why he left but many sources say this :
Tao has been sustaining a lot of injuries in his body. Being an expert in martial arts, Tao has been in charge of Exo’s stunts ranging from back flips and kung fu-inspired moves.
He has also been sustaining a lot of injuries since their debut from all the stunts and choreography. These repeated reports of injury have once again worried fans and has fueled rumors of him possibly leaving once again.
In March 2015, Exo released their sophomore album “Exodus” which spawned the hit single “Call Me Baby”. During the promotional rounds for the album, Tao was evidently missing from their performances as it has been reported that he is seeking treatment for his ankle injury that he got from his appearance in MBC’s “Idol Futsal World Cup” in February 2015.

sources also expressed that:Tao’s father posted a letter in social media site Weibo in April 22, 2015 which stated that he wishes for Tao to leave the group. He cites that the lack of support from SM Entertainment in terms of his recovery from his sustained injuries has compromised his son greatly, thus he believes that leaving the group will serve as the best for Tao.
From then on, Tao went on an abrupt hiatus from Exo and has remained in China for the time being.
Three months after Tao left Exo, it was reported that he was staging a solo debut in China. This was proven true with the release of his first single “T.A.O” in July 2015.
so he honestly just felt he wasn't being taken care of properly

Personally am a huge fan of Exo! and i also love z.tao, I love them so much! I don't hold anything against exo it has nothing to do with the boys it's has everything to do with SM Entertainment.

With all that being said tao started his journey, he changed his stage name to Z.tao made an amazing album in 2015 and I blooming with success today!